Understanding the structure and properties of geological formations can reduce the cost of drilling wells for oil and gas exploration. Measurements made in a borehole (i.e., down hole measurements) are typically performed to attain this understanding, to identify the composition and distribution of material that surrounds the measurement device down hole.
For example, compressional wave velocity measurements can be used to predict pore pressure in non-gas bearing formations, where the pore pressure can be used to determine various characteristics of the formation. However, the presence of gas and total organic carbon (TOC) in the formation can affect measurement accuracy. Pore pressure prediction in these circumstances (e.g., in shale gas formations) may be even more useful, because the pressure can increase from a relatively normal to abnormally high values over a comparatively short depth interval. Thus, pore pressure prediction in shale gas plays may offer even greater challenges than in other types of reservoirs.